The present invention relates to a safety clamp for use with a crane or the like to lift an object, and more particularly to such a safety clamp which is practical for lifting an object in a horizontal position as well as in a vertical position.
A variety of transportation and lifting mechanical devices have been developed, and are intensively used in factories, work places, etc., to lift or move heavy materials. When a crane or the like is used to lift for example steel materials, a clamp shall be used to secure the steel materials to the cable of the crane.
FIGS. 1 and 2 show two clamps for this purpose. The clamp shown in FIG. 1 is for vertical lifting operation. The clamp shown in FIG. 2 is for horizontal lifting operation. These clamps commonly comprises a substantially U-shaped base A, a toothed cam and a swivel jar B mounted in the U-shaped base A for holding down the object to be lifted, a safety spring latch C pressed on the toothed cam to stop the toothed cam in the clamping position, and a hanger D raised from the U-shaped base A for fastening to the cable of the crane.
These conventional clamps have numerous drawbacks as outlined hereinafter:
1) For a horizontal lifting operation or a vertical lifting operation, a different clamp must be used. PA1 2) Due to limited contact area between the swivel jaw and the workpiece, the angle of oscillation of the workpiece must be kept within 10.degree. angle relative to the clamp, and the workpiece will fall from the clamp if the angle of oscillation of the workpiece surpasses 10.degree. angle relative to the clamp. PA1 3) When two clamps are simultaneously used to lift a workpiece in horizontal, the distance between the clamps must be limited because the workpiece falls from the clamps when a lateral force is produced to tile the workpiece over 10.degree. angle. PA1 4) The workpiece tends to fall from the clamp when hit by external means, or when suddenly receiving zero pressure due to an operation error. PA1 5) During lifting, the clamp must be prohibited from receiving a lateral force, and the workpiece tends to be forced away from the clamp if the clamp is hit laterally by an external object.